There is a widerange of opinion
and argument as to when life emerged; in what form, and by what process.There is some evidence, limited conclusions
and much speculation.

Indeed
life on Earth may have originated on another world.This is the hypothesis of 'panspermia' -
that living cells or their pre-cursors might have originated on another world
and hitched a ride to Earth on a meteorite.(For this hypothesis to work, two problems have to be resolved: that
any biological materials being carried by the meteorite can survive severe
heat and survive exposure to radiation).

But
if life emerged on Earth and expressed itself through a process of evolution,
then how did inorganic materials evolve towards life forms?James Trefil, Harold J. Marowitz and Eric
Smith described this as "the great unknown" - when we perceived a
deep gap to exist between inorganic materials and life and believed that
nature must have made a big leap to cross that gap.1They saw the process of evolution
from inorganic materials to early life as working through incremental steps -
a series of "simple, chemical reactions".

Did
life emerge in many forms or in one form?One view is that all of life can be traced back to a single form - the
'last universal common ancestor' or LUCA.Douglas L. Theobald developed a formal test which, he claimed,
provided statistical evidence for the unity of all known life (although this
LUCA may not have been the first organism on Earth).2

Carl
Woese suggested that Darwinian evolution may not have been the original form
of evolution.There may have been an
earlier phase of evolution dominated by horizontal gene transfer (see Mark
Buchanan's 'Another kind of evolution'.)3Carl
Woese proposed also that the three fundamental forms of life which he
identified - Bacteria, Archaea and Eucarya- evolved independently
of each other and not in a line from a common ancestor.4However, Tom A. Williams et al. have argued that 'accumulating
evidence' supports only two primary domains of life.5

Whatever the elements and the processes in the evolution of
life, we may be tempted to assume that life has always evolved towards
greater complexity;but has it?In 2004 a
new virus was discovered - in Bradford! - that was several times larger than any other virus known
previously.It was larger than any
bacteria.It was named as a Mimivirus.6Gary Hamilton reported that it was as
"genetically complicated as some free living organisms" - despite
the common view of viruses as "non-living bags of chemicals.7

Why did the mimivirus have so many genes (almost half of them
unknown previously to science)?.Jean Michel Claverie speculated that the
Mimivirus may have been a descendant of a fully fledged life form that was far
more complex - possibly existing before the emergence of cells while
"nature was still experimenting with simple designs".8

And bigger than the Mimivirus is the Pandoravirus.Two have been isolated so far: one off the
coast of Chile; the other
in a freshwater pond near Melbourne in Australia.They were without "resemblance to any
previously identified virus families".9The largest of the two, the virus isolated in
Chile,
had over 2,500 genes, twice that of the Mimivirus (most common viruses have
few than ten each).

Larger again is the Pithovirus, around 30% larger than the
Pandoravirus.It was first identified
in the Kolmya region of Siberia as the
Northern tundra thawed.Scientists
used amoebas to revive or 'draw out' the virus, which does not harm human or
mouse cells (it appears),10

Viruses qualify as viruses when: they cannot replicate, they
cannot process their own DNA - they have to rely on a host to do that for
them; they cannot make their own energy-storing molecules; they cannot make
proteins; there is no sign of cell division.11

But there may be 'life forms' out there that are stranger
yet.Gary Foster of the University of Bristol, argues that as we "look
at the extremes of life, we will find many more of these strange things.12

Can viruses be considered as a form of life?And what is the role of viruses in the
evolution of life?Luis P. Villarreal
in 'Are viruses alive?'13, wrote that scientists were "beginning to appreciate
viruses as fundamental players in the history of life.He contended, with others, that the cell
nucleus was of viral origins.However,
he acknowledged that viruses existed in a grey area between the living and
the non-living: they could not replicate on their own, but only in living
cells.

What is life?Daniel E.
Koshland observed that a great deal was known about life, but that there was
not general agreement about what life is.14He recalled a scientific conference at which many hours of discussion
on the question "What is the definition of life?" could not resolve
the question.It seemed that everyone
knew what life was ("I'll know it when I see it") but could not
agree on a definition of it.

From the above we may conclude that:

·we
do not know exactly where life on earth began

·we
cannot agree on how life began

·we
cannot say that life evolved in a straight line towards complexity

·we
cannot agree on a definition of life / on what life is

·although
some say that life as we know it has evolved from a single common ancestor,
others have disputed this

But we can say that life is real; that it is there.We can achieve an understanding of how
forms of life develop; and we can form ideas about life and test those ideas.

Kevin
Loughran

2015

1The origin of life, American Scientist.Vol. 97, May-June
2009.p. 206

2A formal text of the
theory of universal common ancestry, Nature.Vol. 465, 13 May 2010.pp. 219-222

3New Scientist.23 January 2010.pp. 34-37

4On the evolution of
cells, Proceedings of the National
Academy of Science of the United States of Americas.Vol. 99, No.. 13,
June 2002.pp. 8742-8747